The present invention relates generally to vehicular vision systems and, more particularly, to a non-circular aperture stop for a reflective or transmissive vision system which reflects or refracts a non-rotationally symmetrical image toward an image capture device, such as a camera or the like. The non-circular aperture stop enhances image sharpness of the image received by the image capture device, while allowing a sufficient amount of light in to the system for effective low light or nighttime conditions.
Typically, a vision system for a vehicle receives an image of a scene occurring exteriorly of the vehicle at a camera and displays the image at a display within the vehicle. In order to control the amount of light being received by the camera, an aperture stop is typically provided along an optical path between the scene and the camera. Historically, optical system aperture stops have been circular due to the rotational symmetry of most optical systems and their ease of fabrication. The amount of light that enters the optical system is then controlled by the transmittance of the materials, the reflectance of the materials and the diameter of the system""s aperture stop. The camera may be a light sensitive, silicon detector array or the like. Because the current signal to noise ratios in commercial detectors limit their effectiveness in nighttime driving scenarios, it is desired to provide as much light as possible to the camera. The circular aperture stop diameter is selected to maximize the light passing through the aperture to the camera, in order to provide effective image reception in nighttime driving conditions.
Because many vehicular vision systems attempt to provide a wide-angle view of the scene exteriorly of the vehicle, the image received by the camera may be distorted. Some of the distortion and other aberrations may be corrected by reducing the diameter of the circular aperture stop. However, although a smaller diameter enhances image sharpness, it also further limits the amount of light being received by the system, and thus detracts from the system""s effectiveness in low light conditions.
Therefore, there is a need in the art for a vehicular vision system which provides a wide-angle image of a scene occurring exteriorly of the vehicle and which functions to enhance image sharpness of the image being received by the camera, while still providing effective nighttime operation of the system.
The present invention is intended to provide a vehicular vision system which provides a compact wide-angle imaging system which is operable to provide enhanced image sharpness of the image received by the system. A non-circular aperture stop is implemented to enhance image sharpness while maintaining the light throughput for nighttime effectiveness of the system. The present invention is especially applicable to vehicular vision systems which include a non-rotationally symmetrical reflective element which reflects a non-rotationally symmetrical image toward an image capture device of the system.
According to one aspect of the present invention, a vision system for a vehicle includes an image capture device adapted to receive an image of a scene occurring exteriorly of the vehicle, a non-circular aperture stop positioned along an optical path between the scene and the image capture device, and a display system which displays an image from an output of the image capture device. The non-circular aperture stop defines a non-circular aperture, through which the reflected image passes. The vision system may further include a reflective element which may reflect a non-rotationally symmetrical image toward the image capture device. The non-circular aperture may be an elliptical aperture or other shaped aperture, depending on the particular application. The vision system may also further include a correcting optic which is positionable along an optical path between the scene and the image capture device and which may include a diffractive element and/or refractive element.
According to another aspect of the present invention, a vision system for a vehicle includes an image capture device, a reflective element, a non-circular aperture stop, and a display system. The reflective element is positionable on a portion of the vehicle and reflects a non-rotationally symmetrical image of a scene occurring exteriorly of the vehicle. The image capture device is adapted to receive the reflected image of the scene occurring exteriorly of the vehicle. The non-circular aperture stop is positioned along an optical path between the reflective element and the image capture device. The non-circular aperture stop defines a non-circular aperture through which the non-rotationally symmetrical reflected image passes. The display system is operable to display an image from an output of the image capture device.
In one form, the non-circular aperture stop comprises an elliptical aperture stop defining an elliptical opening or aperture having a first axis and a second axis with the first axis being larger than the second axis. Additionally, the non-rotationally symmetrical reflective element may have a first radius of curvature and a second radius of curvature, whereby the first radius of curvature is greater than the second radius of curvature. The aperture stop and reflective element are positioned such that the first axis of the elliptical aperture is generally aligned with a first plane defined by the first radius of curvature, while the second axis of the elliptical aperture is generally aligned with a second plane defined by the second radius of curvature, thereby enhancing image sharpness along the second axis of the elliptical aperture.
In another form, the non-circular aperture stop may comprise a non-circular and non-elliptical aperture stop, which defines a non-circular and non-elliptical opening in accordance to an equation derived to optimize the effects of the non-circular and non-elliptical aperture on the image reflected by various non-rotationally symmetrical reflectors. The shape and overall area of the aperture are selected in response to the aberrations and astigmatism of the image being reflected through the aperture stop toward the image capture device. Other shapes of non-circular aperture stops may be selected depending on the shape or curvature of the reflective element.
Therefore, the present invention provides a compact wide-angle vehicular vision system which provides enhanced image sharpness via the non-circular aperture stop. The shape, axes and/or area of the non-circular aperture stop are selected to provide optimal image sharpness, while still allowing a desired amount of light through the aperture to facilitate effective nighttime operation of the vision system.
These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.